Chapter 15 Work, Power, and Simple Machines

15-1 Work *force acting through a distance -Work = force X distance -W = F X d -Units: newton-meter(N-m) or Joule(J)

15-2 Power *how fast work is done -Power = work / time -P = W / t or P = F X d / t

15-2 Power -Units: N-m / s or J / sec or watt (W) -1J/sec = 1 watt watts = 1 kilowatt(kW)

-Horsepower *(hp) = to 750 watts (745.56)

15-3 Machines *device that makes work easier

-effort and resistance -make work easier by changing size or dir of applied force *effort force(F e ): force applied to a machine

-effort and resistance *work input(W i ): work done on a machine -W i = F e X d e Ex: crowbar

-effort and resistance *resistance force(F R ): force applied by the machine *Work output(W O ): work done by a machine

-effort and resistance *resistance distance(d r ): dist through which the object moves -W o = F R X d R -Machines do not multi work, they can multi force -Worko is never greater than worki

-mechanical advantage *(MA) # of times a machine multi the effort force -MA = F R / F E

-mechanical advantage -MA is not always greater than1, sometimes = to 1,

-mechanical advantage -MA of one changes the dir of the effort force -MA is less than 1, increases the dist an object is moved or the speed with which it is moved

-efficiency *comparison of worko to worki - Efficiency = W O / W I X 100 -High eff = worki is changed to worko -eff can never be greater than 100%

-role of friction -less friction = higher its effic -effic can be increased by reducing friction ex: oil, grease, wax,bearings

15-4 Simple Machines -6 simp mach: incline plane, the wedge, the screw, the lever, the pulley, and the wheel and axle

-inclined plane *slanted surface used to raise an object(a ramp) -smaller effort force, but moved through a greater distance

-inclined plane -MA = length of the plane divided by its height -length can never be shorter than its height -MA = never be < 1

-wedge and screws *wedge: incline plane that moves -large force exerted on a small surface

-wedge and screws -longer and thinner the less effort force required ex: sharpening

-wedge and screws *screw: an incline plane wrapped around a cylinder to form a spiral -multi an effort force by acting through a long effort distance -the closer the threads > the MA

-levers *bar that is free to pivot about a fixed point when effort force is applied ex: seesaw, shovel, nutcracker, crowbar *fulcrum: is the fixed point

-levers -3 classes of levers -based on the position of the fulcrum, effort force, resist force

-levers 1)1 st class: multi effort force and also change dir Ex: pliers, scissors, seesaws

-levers 2) 2 nd class: resist force is between the fulcr and the effort force -multi eff force but don’t changed dir Ex: wheelbarrow, door, nutcracker

-levers 3) 3 rd class: eff force > resistan -doesn’t multi force -multi dist of eff force

-levers -MA: # of times the lever increases the eff force *effort arm: dist from the eff force to the fulc *resist arm: dist from resis force to the fulc

-levers -MA = eff arm length resist arm length -1 st and 2 nd levers mult the eff force -3 rd levers multi the distance

-pulleys -can change either dir or amount of eff force -fixed pulley: attached to a stationary object -can’t multi eff force -change dir of eff force

-pulleys -MA of a fixed pulley is 1

-pulleys -movable pulley: -can multi eff force -can’t change dir of an eff force -MA>1

-pulleys -can predict MA by counting the number of supporting sections of rope.

Complex Machines *is a combination of 2 or more simple machines. **you can get no more work out of a machine than you put in it!